Tri-color kinescope



1958 A. M. MORRELL 2,847,600

I TRI-COLOR KINESCOPE 2 Sheets-Sheet 1 Filed Sept. 30, 1953 nTTOR NE 1 g- 1958 A. M. MORRELL 2,847,600

TRI-COLOR KINESCOPE Filed Sept. 30, 1953 2 Sheets-Sheet 2 INVENTOR.

ORNEY TRI-CQLQR KINESCQPE Albert M. Morrell, East Petcrsburg, Pm, assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1953, erial No. 383,340

16 Claims. (Ql. Mil-34) This invention is directed to a cathode ray tube and more specifically to a cathode ray tube having a plurality of electron beams which are converged to a common point at a target electrode assembly.

One type of cathode ray tube which uses a plurality of electron beams is the television picture tube for color of the type disclosed in U. S. Patent 2,595,548, Alfred C. Schroeder. It has been found advantageous in tubes of this type to utilize an electron gun means of the type disclosed in the copending application of Hannah C. Moodey, Serial Number 295,225, filed June 24, 1952. The tube described in this copending application has three electron guns mounted in the neck of the tube envelope symmetrically about the tube axis to provide three substantially parallel beams directed at a target electrode mounted normal to the beam paths. Either an electrostatic or a magnetic electron lens may be used to converge the parallel beams to a common point at the target electrode and in a manner that each beam approaches the target at a small angle of incidence and from a different direction.

The target electrode assembly, of the Moodey application device cited above, includes a masking apertured electrode formed of sheet metal such as a copper-nickel alloy and having a large number of small apertures therethrough. Closely spaced from the surface of the masking electrode remote from the electron guns is a glass sheet having on its adjacent surface a large number of phosphor dots in groups of three, with each dot of each group fiuorescing when struck with high energy electrons with a difierent color of light than the other dots of the group. Each group of three dots is positioned relative to an aperture of the masking electrode so that the center about which the three dots of each group is positioned is aligned with the respective aperture of the mesh. Electrons from the three beams, passing through any one of the apertures in the masking electrode, approach the corresponding group of phosphor dots from their three different directions. In this manner, the

electrons passing through an aperture of the masking electrode along one direction will strike only one phosphor dot for example green fluorescing, and will be prevented by the masking electrode from striking the other two red and blue fluorescing dots of the group. The arrangement provides, then, that an electron beam from each gun of the tube will cause the phosphor screen to luminesce in only one color.

Tubes of the type described have successfully used an electrostatic lens field for converging the electron beams to a common point at the target assembly. The electrostatic lens is tormed between two common accelerating electrodes through which the beams pass. The difference in potential between the electrodes establishes a common converging field having an axis coinciding substantially with the tube axis.

However, the use of such a converging lens field requires that the three electron guns be quite accurately disposed symmetrically about the axis of the lens field 2,847,660 Patented Aug. 12, 1.958

so that the three beams will pass through identical portions of the lens field to provide convergence of the three beams to a single point. Accurate convergence of the three beams also depends upon precise alignment of each gun and the gun parts. Misalignment oi the parts of a gun results in the displacement of the beam from its path of optimum beam convergence. A single electrostatic converging lens field, of the type described, has no separate control of each beam so as to correct for misalignment of gun parts which inherently occurs in tubes of the type described. This requires additional devices for correcting the eifect of misalignment of the beams and to provide correct convergence of the beams at the target. These devices, such as individually mounted permanent magnets mounted on the tube neck, usually cause a distortion of the beam and hence reduce resolution.

In the copending application of Albert M. Morrell, Serial No. 364,041, filed on June 25, 1953, now Patent 2,752,520, issued June 26, 1956, there is disclosed a tube utilizing magnetic convergence, in which a pair of pole pieces were inserted on either side of each beam path to provide, during tube operation, a magnetic field in the path of each beam which directed the beam toward the axis of the tube. By adjusting the field strength between each pair of pole pieces, the three beams could be converged substantially to a common point on the tube axis and at the target of the tube.

it has been found that an improvement of this tube design has been achieved by mounting the three electron guns at an angle to the tube axis so that the physical alignment of the three guns was such to cause the three electron beams to converge at a common point on the target. However, due to any misalignment of the gun parts, as well as other factors, the three beams will not necessarily coincide at the same point on the tube target. The pole pieces on either side of each beam path and previously used for convergence can be also used to correct for misalignment of gun parts. Furthermore, an additional pair of magnetic pole pieces is used to correct for non-convergence of the beams by the magnetic pole pieces.

It is, therefore, an object of this invention to provide a cathode ray tube having a plurality of electron beams which can be controlled for accurate convergence on the target of the tube.

It is another object of the invention to provide a color television tube utilizing a plurality of electron beams Whose convergence to the target can be independently controlled.

it is a further object of the invention to provide a color television tube having a plurality of electron beams the direction of which can be independently controlled together with means for correcting the convergence of the beams at the target of the tube together with means for correcting the convergence of the beams.

The invention makes use of magnetic converging means for adjusting the convergence of the three beams of a color tube to any common point on the target electrode assembly. Independent convergence control is provided by a plurality of pairs of pole pieces extending transversely of and on opposite sides of each beam path. Portions of the pole pieces are positioned adjacent the envelope neck of the tube whereby an electromagnet mounted on the tube neck adjacent each pair of pole pieces will establish a magnetic field across each beam path to change the convergence of the electron beam toward the axis of the tube. By adjusting the magnetic field between each pair of pole pieces, the three electron beams can be brought to substantially any common point on the target of the tube. An additional pair of pole pieces is mounted adjacent one of the three guns 3 to provide a correcting magnetic field at right angles to the other field of that gun so that convergence of the three beams can be obtained in spite of any misalignment of gun parts which produces misconvergence of the beams at the target.

Figure l is asectional view of a cathode ray tube utilizing the invention.

Figure 2 is an enlarged perspective view of a portion of the target of the tube in Figure 1.

Figure 3 is an enlarged sectional view of part of the gun structure of the tube of Figure 1.

Figure 4 is a cross sectional view along line 4-4 of Figure 3.

Figure 5 is a cross sectional view along line 5'5 of Figure 3.

Figure 6 is a schematic representation of beam convergence at the target electrode of the tube of Figures 1-5.

Figure 1 discloses a cathode ray tube having a plurality of electron beams and used as a picture viewing tube for color television. The tube consists of an evacuated envelope having a neck portion it) of glass, for example, and a shell portion 12 which may be either conical or substantially the frustum of a pyramid, as is well known in the art and which may be of metal or glass. Within the neck portion of the envelope are three electron guns 13 shown in greater detail in Figure 3. The guns 13 each consists of a cathode electrode 14- mounted within a tubular control. grid electrode 16. Each control grid 16 is closed at one end by a wall having a single aperture at its center. The adjacent end of each cathode tube 14 is closed by a solid wall portion and is coated on its outer surface with electron emitting material, such as a mixture of barium and strontium oxides, to provide a source of electron emission.

Closely spaced from the control grid 1.6 of each electron gun and along a common axis, there is mounted a short tubular or cup-like accelerating electrode 20 having an aperture in the bottom of the cup in line with the aperture in the control grid wall 15. Spaced along the axis of each gun from accelerating electrode 20 is a relatively long tubular accelerating electrode 22, closed at its end facing accelerating electrode 20 by an apertured wall portion 23, whose aperture is also aligned with the apertures in electrodes 20 and 16. Closely spaced from the other ends of electrodes 22 is a common focusing electrode 24, consisting of a tubular member closed by an apertured wall portion 26 at the far end and having mounted in the opposite wall portion 28 a plurality of short tubular members 30. One of the tubular members 30 is aligned on the common axis of each electron gun with the other electrodes 16, 20 and 22 respectively. Within the wall 26 of tubular electrode 24, there is formed an aperture 32 on the axis of each gun and also in alignment with the apertures of electrodes 16, 20 and 22. Tubular electrode 24 is supported from and electrically connected by spring fingers or spacers 34 to the wall of the envelope neck 10. The spring fingers make electrical and physical contact with a conductive wall coating 36, which extends over the inner surface of the tubular envelope neck portion 10 from electrode 24 into the conical envelope portion 12 to make contact with the metal shell 12.

The several electrodes are mounted within the neck portion 10 by rigidly fastening them together by means of a plurality of glass mounting rods 38. Each electrode has several studs welded at one end to the electrodes and sealed at the other end into a glass rod 38 in a conventional manner. Lead wires 42 extend from each electrode respectively, to supporting base wires (not shown) sealed through the base 43 of the tubular envelope neck portion 10 in a conventional manner. The base wires are conductively fixed to base pins 45 extending through base 43 to make electrical contact to external sources of potential. By lead wires 42 and the spring spacing fingers 34, the electron guns are rigidly supported within the envelope neck portion 10.

In Figure 3, voltages are indicated as those which are applied to the respective gun electrodes. These voltages are those which have been successfully used in tubes of the type described and need not be limiting.

During the operation of the several electron guns, potentials are applied to several gun electrodes as indicated. The electron emission from each cathode 14 is formed by electrostatic fields respectively between electrodes 16, 20, and 212 into an electron beam directed through the apertured portions of the gun electrodes. The difference of potential between electrodes 22 and the corresponding electrode portions 30 provide a principal focusing lens field in the path of each electron beam, whereby the electrons of each beam are converged to a fine focus at the target electrode assembly 44 mounted in the large shell portion 12 of the envelope.

Target assembly 44 consists of a glass support plate 46 and a metallic masking electrode 48 closely spaced from the surface of plate 46 facing the electron guns. Masking electrode 48 is a thin copper-nickel sheet having a large number of small apertures 50. Fixed to the adjacent surface of the glass plate 46 is a luminescent screen consisting of groups of phosphor dots 52, with each group consisting of three dots positioned in a triangular arrangement about a center point 54, as shown in Figure 2. The positioning of each group of phosphor dots is such that the center of each aperture 50, in the masking electrode 48, will be aligned with a point 54 of the corresponding group of phosphor dots.

The phosphor dots 52 of each group are formed of phosphor material fluorescing with a different colored light when struck by the high energy electrons from guns 13. As indicated in Figure 2 the dots of each group have a red, green, or blue fluorescence under electron bombardment and indicated respectively by R, G, and B. Furthermore, the positioning of the phosphor dots 52is that in which each dot is aligned with its corresponding aperture 50 in electrode 48 along a diiferent directional line X, Y, and Z, respectively. The fluorescent screen is covered with a thin film 53 of reflective metal to intensify the luminescence of the phosphor by reflecting light from the phosphor screen through plate 46 toward the observer.

The three electron beams leaving the electron guns 13 are caused to converge toward the common axis 17 of the tubular envelope portion 10 by mounting each gun 13 at a small angle to axis 17 so that the axes of the three guns will converge to a common point on the masking electrode 48. Thus, each beam, normally following the axis of its gun, will approach the masking electrode 48 at a small angle of incidence and from one of the difierent directions X, Y, or Z. Electrons from each beam passing through the apertures 50 of electrode 48 along one of the paths extending in the directions X, Y, or Z, will strike the phosphor dot in each group of dots. The arrangement is such that the electrons from each gun can strike only those phosphor dots 52 luminescing with a single color of light. The angle which each gun makes with tube axis 17 is small and is determined by the dimensions of the tube. In tubes of the type described which have been successfully operated, this angle is in the order of 1 10'. The Figure 3 exaggerates the angle between the guns and axis 17 for purpose of illustration.

The three beams are simultaneously scanned over the surface of the masking electrode 48 by conventional scanning means indicated as a neck yoke 56, which consists of two pairs of deflecting coils, with the coils of each pair mounted on opposite sides of the envelope neck 10. Each pair of deflecting coils of yoke 56 is connected in series to sources of saw tooth currents for providing line and frame scansion of the three electron beams simultaneously over the surface of the masking electrode 48. The scanning coils of yoke 56 are conventional and do not constitute a part of this invention and need not be further described. The scansion of electron beams may be in any desired manner but for color television viewing is as a rectangular raster. The operation of tubes of the type described are more fully set forth in copending application Serial Number 231,925, filed June 16, 1951, by Harold B. Law, now U. S. Patent No. 2,663,821.

As the three beams are simultaneously scanned over the surface of target electrode assembly 44, the beams which normally have convergence on the axis 17 of the tube will lose convergence at the target, since the distance of beam convergence from masking screen 48 varies due to the geometry efiects connected with the deflection of several converging beams. It is thus necessary to provide a dynamic magnetic field in the path of each beam by a plurality of coils 66 (Figs. 3 and 4). Also, because of the complexity of using three beams, the convergence of any two beams is different than the convergence of any other two of the three beams during scansion of all three beams across target electrode assembly 44. Because of this reason, it is necessary to apply different dynamic correcting voltages to each of the three coils 66 to continuously provide common convergence of all three beams at the masking electrode 48 during the scanning of the rectangular raster. This expediency is known as dynamic convergence. Such a result would be unobtainable to the same degree with electrostatic convergence of the three beams, as only a single dynamic voltage could be applied between the electrodes providing the converging electrostatic field. The correcting magnetic field is established respectively in the path of each beam and the strength and direction of each field is varied in synchronism with the deflection of the beam so that the three beams at all times may be converged to a common point during the scanning of the beams over the surface of the apertured mask 48.

The dynamic converging means consists of pairs of pole pieces 57 mounted on opposite sides of the electron beam paths. As shown specifically in Figures 3 and 4, the pole pieces include parallel portions 58 extending substantially radially to the axis 17 of the envelope neck 10. The pole pieces 57 are fixed through the wall of the tubular electrode 24 and adjacent to the beam focusing extensions 30. Furthermore, pole pieces 57 have arcuate portions 60 extending along the inner wall portions of the tubular neck It) and as shown in Figure 4. The arcuate pole pieces portions 60 are matched with arcuate portions 62 of armatures 64 forming a part of the electromagnet 66 mounted on the outer wall portion of the tubular neck 10. The parallel plate portions 58 of each pair of pole pieces 57 extend on opposite sides of each electron beam path.

The operation is such that each electron beam will pass between a pair of pole portions 58 during tube operation. Magnets 66 comprise single coils for providing the dynamic convergence of the electron beams to any common point on the masking electrode 48. The passage of current through coils in the magnet coils 66 will cause deflection of the corresponding electron beam in a direction parallel to the plate portions 58. With the correct polarity given to the plates 58 of each pair of pole pieces, the field established between plates 58 will direct the corresponding electron beam radially toward or away from the axis 17 of the tube.

Due to any misalignment of the gun parts as well as non-uniformity of any field aflecting the beams, the three beams may not normally coincide accurately at the same point. Figure 6 indicates that if the three beams are accurately positioned symmetrically about axis 17, and with no deflection fields acting on the beams, they will strike a single spot 0 on axis 17. However, due to misalignment of gun parts or non-uniformity of fields through which the beams pass or both, one or more of the spots R, B

and G may be displaced from the spot 0, which they all should theoretically strike and will strike in new spots R, G and B, for example. The action of the fields between corresponding plates 58 now is to move the three spots R, B and G together along the lines 61, 63 and 65 respectively, and as indicated by the arrows as shown in Figure 6. However, the three beams can not now be converged to a single common point, although any two beams can always be brought to the same spot.

Accordingly, then a correction is introduced into the deflection of one of the beams by a magnetic field established between pole pieces 70 and 72 as shown in Figures 3 and 5, for example. In accordance with the invention, pole pieces 70 and 72 are fixed to the tubular electrode 22 of the blue gun 13 and are mounted at substantially right angles to the corresponding plates 58 of the gun. A magnetic field between the parallel pole pieces 70 will introduce a beam deflection at right angles to that pro duced by plates 57 on the same beam. As shown in Figure 6, this produces a resultant deflection of the beam B along the path of arrow 63, so as to shift the position of B to the intersection of spots G and R and to provide a common convergence of all of the beams at the point 0. The point 0 is not greatly displaced from the theoretical point 0, but the displacement is a small shift of the beams which can be compensated for by other means during tube operation. However, it is within the scope of this invention to use pole pieces 70 and 72 for each beam, it necessary or desirable.

The correcting magnetic field established between parallel pole pieces 70 and 72 may be formed in accordance with the invention by extending the pole piece 70 adjacent to the neck portion of the tube envelope to form flanged end portions 73. Pole piece 72 is a box-like construction and the wall of the box opposite gun electrode 22 is arcuate to follow the curvature of the tube neck 10. Armature portions 74 of an armature 76 are positioned on the outer surface of the tubular neck portion 10 overlying the flanged pole piece portions 73. Armature 76 extends through an activating coil winding 7'25 to median pole piece portion 75 overlying internal pole 72. The polarity of the armature portions 74 and 75 can be established respectively by the current flow through the magnetic coil winding 78, which in turn establishes the magnetic correcting field between the pole pieces 70 and 72. The strength of this field can be varied by the amount of current passed through the coil 73. A permanent magnet with a variable shunt or other controlling device may be used in place of electromagnet 73.

in the above-noted application of Albert Morrell, the internal pole pieces for correcting the beam position on the blue gun are mounted through slits in the sides of the accelerating electrode cylinder. However, in this application and in accordance with the invention, the corrector pole pieces 70 and 72 are fixed by welding, for example, to the external surface of accelerating electrode 22. Such a novel assembly is much easier to manufacture and assemble. Furthermore, the magnetic field produced between the pole pieces 70 and 72 is more closely perpendicular to each pole face because of the symmetry of the pole pieces. Normally, within the accelerating electrode 22 there is positioned an apertured disk 77, which is used to limit the dispersion of the electron beam and to permit the more parallel electron rays at the center of the beam to pass through the gun. By placing the pole pieces 70 and 72 external to the electrode cylinder 22, there is no interference with the limiting aperture 77. A further advantage of the novel design of the pole pieces 70 and 72 is the facility of providing the matching external armature 76. This armature forms an E-shaped core. The arcuate design of the armature 76 is simple and relatively easy to form.

The pole pieces 58 and 70 as well as the armature portions 60, 62 and 64 are made of high magnetic permeability metal, while the supporting members and other parts of guns 13 are made of non-magnetic material.

,While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications maybe made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron discharge device comprising an envelope having a tubular portion, an electron gun mounted within said tubular envelope portion, said gun including a plurality of electrodes mounted along a common axis for forming a beam of electrons, a pair of magnetic pole pieces mounted externally on one of said electrodes for forming a magnetic correcting field in the path of said electron beam, said pole pieces including an elongated member extending across said tubular envelope portion and having end portions positioned adjacent the wall of said tubular envelope portion and a second pole piece member fixed to the opposite side of said tubular electrode from said elongated member, said second pole piece member having an arcuate portion extending adjacent to the wall of said tubular envelope portion.

2. An electron discharge device comprising an envelope having a tubular portion, an electron gun mounted within said tubular envelope portion, said gun including a plurality of electrodes mounted along a common axis for forming a beam of electrons, a pair of magnetic pole pieces mounted externally on one of said electrodes for forming a magnetic correcting field in the path of said electron beam, said pole pieces including a flat plate extending across said tubular envelope portion and having flanged edge portions positioned adjacent the wall of said tubular envelope portion and a tubular pole piece member fixed to the opposite side of said tubular electrode from said flat plate, said tubular pole piece having an arcuate wall extending adjacent to the wall of said tubular envelope portion, a magnet coil mounted on said tubular envelope portion, and an armature extending through said coil and having end portions adjacent the .Wall of said tubular envelope portion and overlying said adjacent portions of said pole pieces respectively.

3. An electron discharge device comprising an envelope having a tubular portion, an electron gun mounted within said tubular envelope portion, said gun including a plurality of electrodes mounted along a comm-on axis for forming a beam of electrons, a pair of pole pieces mounted externally on one of said electrodes for forming a magnetic correcting field in the path of said electron beam, said pole pieces including a flat plate extending across said tubular envelope portion and having flanged edge portions positioned adjacent the wall of said tubular envelope portion and a tubular pole piece member fixed to the opposite side of said tubular electrode from said flat plate, said tubular pole piece having an arcuate wall extending adjacent to the wall of said tubular envelope portion, a magnet coil mounted on said tubular envelope portion, and an armature extending through said coil, said armature including a median portion thereof mounted on said tubular envelope overlying said arcuate wall of said tubular pole piece and end portions extending to the wall of said tubular envelope portion, each of said armature end portions being flanged and overlying one of said flanged edge portions of said flat plate pole piece.

4. An electron discharge device comprising a plurality of electron guns, each of said electron guns including a plurality of electrodes insulatingly spaced along an axis, means mounting said electron guns with their axes converging, said electrodes of each of said guns including portions for forming and accelerating an electron beam along a path coinciding with the axis of said respective gun, and a different pair of magnetic pole pieces positioned on opposite sides of the axis of each of said electron guns for establishing a magnetic field between said 8 different pair of pole pieces and transverse to said respective beam path to adjust the convergence of said electron beams.

5. An electron discharge device comprising a plurality of electron guns, each of said electron guns including a plurality of electrodes insulatingly spaced along an axis, means mounting said electron guns with their axes converging, said electrodes of each of said guns including portions for forming and accelerating an electron beam along a path coinciding with the axis of said respective gun, a difierent pair of magnetic pole pieces positioned on opposite sides of the axis of each of said electron guns for establishing a magnetic field between said different pair of pole pieces and transverse to said respective beam path for adjusting the convergence of said electron beams, and a pair of magnetic pole pieces mounted 011 one of said guns for forming a magnetic correcting field in the path of said electron beam and having a direction at an angle to the direction of the respective convergence field of said one gun.

6. An electron discharge device comprising, electron gun means including a source of electrons for providing a plurality of electron beams along converging paths, a plurality of pairs of pole pieces, and means mounting a different pair of said pole pieces on opposite sides of each beam path for establishing a magnetic field therebetween transverse to said respective beam path.

7. An electron discharge device comprising a plurality of electron guns, each of said electron guns including a plurality of electrodes insulatingly spaced along an axis, means mounting said electron guns with their axes converging, said electrodes of each of said guns including portions for forming and accelerating an electron beam along a path coinciding substantially with the axis of said gun, a target electrode mounted transversely to said beam path, means for simultaneously scanning said electron beam over a surface of said target electrode, and a different pair of magnetic pole pieces positioned adjacent to the axis of each of said electron guns to adjust the convergence of said electron beams during scansion over said target electrode.

8. An electron discharge device comprising an envelope having a tubular portion, a plurality of electron guns, each of said electron guns including a plurality of electrodes insulatingly spaced along an axis, means mounting said electron guns with their axes converging, said electrodes of each of said guns including portions for forming and accelerating an electron beam along a path coinciding substantially with the axis of said gun, a target electrode mounted transversely to said beam path, means for simultaneously scanning said electron beams over a surface of said target electrode, and a difierent pair of magnetic pole pieces positioned adja cent to the axis of each of said electron guns to adjust the convergence of said electron beams during scansion over said target electrode, a pair of magnetic pole pieces mounted externally on one of .said electrodes for forming a magnetic correcting field in the path of said electron beam, said pair of magnetic pole pieces having portions extending adjacent to the wall of said tubular envelope to be coupled to a magnetic flux exterior of said envelope wall.

9. An electron gun for a cathode ray tube, said gun comprising an electron source and a plurality of electrodes mounted along a common axis for forming a beam of electrons, a first pair of magnetic pole pieces having plate portions mounted substantially parallel on opposite sides of said gun axis, and :a second pair of magnetic pole pieces having plate portions mounted on opposite sides of one of said electrodes and in planes substantially perpendicular to said portions of said first pair of magnetic pole pieces, said second pair of magnetic pole pieces having an arcuate wall to be coupled to a magnetic flux.

10. An electron gun for a cathode ray tube, said gun comprising a plurality of electrodes mounted in spaced relationship along a common axis, a pair of pole pieces mounted on one of said electrodes and including a fiat plate extending in a plane parallel to said axis, and a tubular pole piece member fixed to the opposite side of said one electrode from said flat plate.

11. An electron gun structure for a cathode ray tube, said gun comprising a plurality of electrodes mounted in spaced relationship along a common axis, said plurality of electrodes mounted in spaced relationship along a common axis, said plurality of electrodes including a tubular electrode coaxial to said common axis, a pair of pole pieces mounted on said tubular electrode, said pole pieces including a flat plate extending in a plane parallel to said axis and having flanged edge portions spaced from said tubular electrode, and a tubular pole piece fixed to the opposite side of said one electrode from said flat plate.

12. An electron discharge device comprising a plurality of electron guns, each of said electron guns including a plurality of electrodes insulatingly spaced along an axis, means mounting said electron guns with their axes converging, said electrodes of each of said guns including portions for forming and accelerating an electron beam along a path coinciding with the axis of said respective gun, a diiferent pair of magnetic pole pieces positioned on opposite sides of the axis of each of said electron guns for establishing a magnetic field between said different pair of pole pieces and transverse to said respective beam path to adjust the convergence of said electron beams, and means for establishing a second magnetic field transverse to one of said beam paths and at an angle to the field between said difierent pair of pole pieces on opposite sides of said one beam path.

13. An electron discharge device comprising, electron gun means including a source of electrons for providing a plurality of electron beams along converging paths, a plurality of pairs of pole pieces, means mounting a different pair of said pole pieces on opposite sides of each beam path for establishing a magnetic field therebetween transverse to said respective beam path, and means for establishing a second magnetic field transverse to one of said beam path and at an angle to the field between said different pair of pole pieces on opposite sides of said one beam path.

14. An electron discharge device comprising an envelope, electron gun means within said envelope for producing separate electron beams along three paths not in a common plane and extending in the same general direction, a magnetically permeable plate structure mounted within said envelope and extending between one of said three electron beam paths and the other two of said beam paths, a magnet including two pole structures mounted with one of said pole structures closely spaced from one end of said plate structure and the other of said pole structures having one portion thereof closely spaced from and on the side of said one electron beam path opposite to said permeable plate.

15. An electron discharge device comprising an envelope having a tubular portion, an electron gun structure within said envelope tubular portion for producing separate electron beams along three paths not in a common plane and extending in the same general direction as the axis of said tubular portion, a magnetically permeable plate structure mounted Within said tubular envelope portion and extending between one of said three electron beam paths and the other two of said beam paths, said plate structure having an end portion terminating adjacent to the inner surface of said tubular envelope portion, a magnet including two pole pieces mounted with one of said pole pieces closely spaced from said end portion of said plate structure and the other of said magnet pole pieces closely spaced from and on the side of said one electron beam path opposite to said permeable plate.

16. An electron discharge device comprising an envelope, a plurality of electron guns Within said envelope for producing separate electron beams along a plurality of paths extending in the same general direction, a magnetically permeable plate structure fixed and extending between said one of said electron guns .and the remainder of said electron guns, said plate structure having an end portion terminating adjacent to said envelope wall, a magnet including two pole pieces mounted externally of said envelope with one of said pole pieces closely spaced from said end portion of said plate structure and the other of said pole pieces having one portion thereof closely spaced from and on the side of said one electron gun opposite to said permeable plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,460,609 Torsch Feb. 1, 1949 2,522,872 Heppner Sept. 19, 1950 2,689,922 Francken Sept. 21, 1954 2,691,115 Jenny Oct. 5, 1954 

